A recording element comprising a photopolymerizable composition on a support is already known, and has been mainly used as a presensitized printing plate. The recording element is usually used in an image forming method which comprises the steps of: imagewise exposing to light the recording element to polymerize the photopolymerizable composition within the exposed area; and washing the element with a solvent to remove the unpolymerized photopolymerizable composition.
U.S. Pat. Nos. 4,399,209, 4,440,846 and 4,663,266 disclose improved recording elements, in which a photopolymerizable composition is contained in microcapsules which are dispersed in a recording layer. The recording element employing the microcapsules can be used in an image forming method which comprises the steps of: imagewise exposing to light the recording element to polymerize the photopolymerizable composition within the exposed area; and pressing the recording element to rupture the microcapsules containing the unpolymerized photopolymerizable composition. This image forming method contains no process of washing the element with a solvent. It is advantageous for the recording element employing microcapsules to give an image only by the dry process.
However, in the recording element employing the microcapsules, the active components of a photopolymerizable composition such as a polymerizable compound and a photopolymerization initiator are together contained in the microcapsules. If the recording element is exposed to light by accident, the exposed element is of no use, since a polymerization reaction has been initiated with light. There is another problem that where the active components are arranged in contact with each other, they tend to be inactivated. For example, where a photopolymerization initiator is dissolved in a polymerizable compound, the initiator gradually precipitates from the polymerizable compound and is then inactivated.
U.S. Pat. No. 4,636,453 (Keys et al.) discloses a photopolymerizable element comprising a support, a photopolymerizable composition layer and a protective layer. In the photopolymerizable composition layer, pressure rupturable microcapsules containing at least one active component for the photopolymerizable composition are dispersed. In other words, the photopolymerizable layer contains at least two active components of a photopolymerizable composition, said components being separated from each other by the shell of microcapsules in such manner that at least one component is contained in the microcapsules and the other component is arranged outside of the microcapsules.
FIG. 4 is a sectional view schematically illustrating an embodiment of the photopolymerizable element disclosed in U.S. Pat. No. 4,636,453.
As is shown in FIG. 4, the photopolymerizable element comprises a support (41), a photopolymerizable composition layer (43) and a protective layer (44). A polymerizable compound is contained in microcapsules (42) which are dispersed in the composition layer (43). A photopolymerization initiator (o) is arranged outside of the microcapsules (42).
The photopolymerizable element disclosed in U.S. Pat. No. 4,636,453 is used in an image forming method which comprises the steps of: pressing the element to form the photopolymerizable composition in the composition layer, said composition being formed by the rupture of the microcapsules; imagewise exposing to light the element to polymerize the photopolymerizable composition within the exposed area; and washing the element with a solvent to remove the unpolymerized photopolymerizable composition.
FIG. 4-A is a sectional view schematically illustrating the process for pressing the element.
As is shown in FIG. 4-A, the element is pressed to rupture the microcapsules (45). Thus, the photopolymerization initiator (o) is mixed with the polymerizable compound contained in the microcapsules to form a photopolymerizable composition.
FIG. 4-B is a sectional view schematically illustrating the process for imagewise exposing to light the element.
As is shown in FIG. 4-B, the photopolymerizable composition is polymerized within the exposed area (46), while the photopolymerizable composition is not polymerized within the other area (47).
FIG. 4-C is a sectional view schematically illustrating the process for washing the element with a solvent.
As is shown in FIG. 4-C, the unpolymerized photopolymerizable composition is removed by the solvent. Thus, a polymer image (48) is obtained.
In this photopolymerizable element, the active components of a photopolymerizable composition are separated from each other by the shell of the microcapsules. Accordingly, even if the element is exposed to light by accident, no polymerization reaction is initiated with light. Therefore, the above-mentioned problems of the recording element which employs the microcapsules containing all of active components of a photopolymerizable composition have been solved by the use of this element.
But, according to the image forming method disclosed in U.S. Pat. No. 4,636,453, the element should be pressed to rupture all of the microcapsules prior to the process for imagewise exposing to light the element. Accordingly, the method should contain a wet process for washing the element with a solvent. In other words, this image forming method loses the merit of the microcapsules (i.e., dry process) mentioned in U.S. Pat. Nos. 4,399,209, 4,440,846 and 4,663,266.